1. Field of the Invention
This invention relates to a network protector and, more specifically, to a network protector which incorporates laminated line buses and load buses.
2. Description of the Prior Art
Secondary power distribution networks consist of interlaced grids which are supplied by two or more sources of power so that the loss of a single source of power will not result in an interruption of service. Such networks provide the highest level of reliability possible with conventional power distribution and are normally used to supply high-density load areas such as a section of a city, a large building, or an industrial site. Between the power sources and the network is a transformer and a network protector. The network protector consists of a circuit breaker and a control relay. The control relay senses the transformer and network voltages and line currents and executes algorithms to initiate breaker tripping or closing action. Trip determination is based on detecting an overcurrent condition or reverse power flow, that is, power flow from the network to the energy source.
Network protectors are often found in dust-proof or moisture-proof housings which are disposed in subterranean passageways in large metropolitan areas. The lineside and loadside busses are mounted inside the housing. To prevent the electrical buses from contacting water in the event of a flood, the lineside terminals and the loadside bus terminals extend upwardly towards the top on the housing. Connectors are coupled to the busses through opening near the top, or on the top, of the enclosure. Electrical buses connecting the circuit breaker to the transformer and the circuit breaker to the load were constructed with a hollow square cross-section in order to increase the surface area, and therefore the emissivity, of the bus. This shape also allowed air to flow through the bus and remove heat by convection. The square tubular busses made by a single manufacture which is located in France. As such, the square tubular busses must be imported and availability is subject to the manufacturer. Additionally, the square busses were designed to cooperate with a rollout circuit breaker, and will not accommodate a drawout breaker. Drawout circuit breakers are now preferred because of safety of operation and maintenance. Drawout circuit breakers cannot fit within the housing due to the shape of the busses.
The use of thinner busses would be desirable; however, due to the amount of current flowing through the buses (greater than 2000 amps) solid, flat bus bars may not be used. Solid bus bars do not have a sufficient emissivity to meet the temperature rise specification. That is, due to the current flowing through the buses, the temperature of a flat bus bar would be above the 140xc2x0 C. rise criteria, which is unacceptable. Such high temperatures would place thermal stress on the bus and eventually allow the bus to degrade prematurely.
There is, therefore, a need for a thin bus for a network protector which does not result in an excessive bus temperature.
There is a further need for a reduced length bus for a network protector which may be used with a drawout circuit breaker.
These needs and others are satisfied by the invention which provides network protector buses constructed of multiple, spaced laminations. Multiple laminations allow the bus to have a sufficient surface area to allow cooling to occur despite the reduced width. With a reduced bus width, a drawout circuit breaker may be located within the network protector housing. The width occupied by the electrical buses may further be reduced by coating the buses with a dielectric epoxy, thereby allowing the loadside buses and the lineside buses to be nested together. The epoxy coating also increases the emissivity of the bus surface thereby reducing the heat buildup.